"So I think it's something that had to be done", Mr Trump said.
CNBC has described the withdrawal of Brennan's security credentials as "more of a political than practical move".
Trump also threatened to yank the clearances of eight former officials and a current one, mostly top intelligence and law enforcement officials from the Obama and previous administrations.
All are critics of the president, or are people Mr Trump appears to believe are against him.
Here is a sampling of some of the reactions from top Democrats, lawyers, and national security experts.
"Russia, if you're listening, I hope you're able to find the 30,000 emails that are missing", Mr. Trump said in a campaign speech. Trump's statement, distributed to reporters, was dated July 26, 2018, suggesting it could have been held and then released when needed to change a damaging subject.
The initial White House statement about Brennan's clearance made no reference to the Russian Federation investigation.
The names amount to an unofficial enemies list for this White House. He said Brennan of participated in a "shredding of constitutional rights, lied to Congress and has been monetizing and making partisan political use of his clearance since his departure".
In response, Brennan said on Wednesday that Trump's decision to revoke his security clearance was part of an effort to silence critics.
Sanders is citing Brennan's "erratic conduct and behavior" and accusing him of "lying" and "wild outbursts".
"Mr Brennan's lying and recent conduct characterised by increasingly frenzied commentary is wholly inconsistent with access to the nations' most closely held secrets", Mr Trump said. The President spent most of the last week on a working vacation at his property in Bedminster, New Jersey.
Brennan also tweeted out against the move on Wednesday.
He also likened the action to things he had seen from "foreign tyrants, despots, and autocrats" throughout his career. Trump said. "So I think something had to be done".
The White House did not claim that Brennan gave away classified information or national secrets.
The White House has said that Turkey's tariff hikes on United States products in retaliation for sanctions against Ankara were "regrettable" and again called for the immediate release of American pastor Andrew Brunson.
Trump also said he is reviewing the security clearances of other Barack Obama administration officials he has accused of trumping up Russian Federation allegations in a bid to undermine his presidency.
FILE PHOTO: Former CIA director John Brennan testifies before the House Intelligence Committee to take questions on "Russian active measures during the 2016 election campaign" on Capitol Hill in Washington, U.S., May 23, 2017.
Ohr is the only current government employee on the list.
Officials at risk of seeing their security clearances revoked expressed concern about Trump using his presidential authority to strike back at critics but said revoking their security clearances would have little impact on them.
The Steele dossier was also presented as another reason to revoke Brennan's clearance, according to Trump's written statement.
"Today, in fulfilling that responsibility, I have made a decision to revoke the security clearance of John Brennan, former Director of the Central Intelligence Agency", the statement read. He has been critical of Trump and told CNN on Wednesday that he has no plans to stop speaking out when he's asked for his views on the Trump administration.
Clapper said he and the others targeted had all "directly run afoul" of Trump and his administration in some way.
When asked about the impact of the USA spat with Turkey on the country's currency, the spokeswoman said Washington was "monitoring the situation".